Presently, discs for use in disc drives are formatted to contained servo information and data in a variety of ways. One of the most common formats used with drives with multiple discs is that of a dedicated servo surface. In such an arrangement, one of the surfaces of one disc is dedicated for containing a high frequency of servo information, which information allows the read/write registration head to be maintained continuously on a track (track registration) and also which is used for seeking new track locations.
Another format which is often used is that of a single or a multiple servo sector design whereby servo information is associated with a block of data. In a single servo sector format, each track or cylinder of the disc has a single field which serves as a servo field and one or more fields which serve as data fields. In formats having multiple servo sectors, there are a multiplicity of servo fields which are spaced about the disc, each associated with one or more data fields. The servo fields on all of the tracks are radially aligned as are the data fields. Such alignments of the servo fields is highly advantageous in order to simplify head centering or registration and seek functions.
A disadvantage of such an arrangement is that there is inefficient use of space for storing data. Generally, the same amount of data is stored on the inner as well as the outer track. Thus, the density of the transitions on the outer track is much less than the density of the transitions on the inner track, resulting in an inefficient use of the storage capacity of the disc on the outer tracks.
Quite recently, a zone recording format has been employed in practice which clusters the tracks or cylinders into two or more concentric zones such as an outer zone, one or more middle zones and an inner zone. Each of these zones is packed with a number of sectors containing data, which sectors are equally spaced around the track. Generally, the tracks in the outer zone would have the highest number of equally spaced sectors. The middle zones would have the next highest number of equally spaced sectors. The inner zone would have the lowest number of equally spaced sectors. Such an arrangement, as can be appreciated, is highly advantageous as each of the tracks from the outer most track to the inner most track can be packed with the optimal number of transitions per inch, greatly increasing the storage capacity of the disc media of the disc drive.
Such an arrangement, however has a disadvantage in that only the starting point of each of the first sector of each track can be aligned across different zones. Such an arrangement is thus highly disadvantageous in obtaining servo information along the entire track in order to assist in the head seeking operation which involves crossing zones. Only one reference per revolution is available for servo synchronization.